Water slow to heat and not hot enough...

- Water gets hot slower as you get farther away from the water heater. However, none of outlets produce hot water anywhere near instantly.

- Compared to having just one outlet on, the water gets hot faster (about 30 seconds) and reaches a hotter maximum temp. when two or more water outlets run at the same time. But when the additional outlets are shut-off, the maximum temp. of the hot water decreases.

- The maximum hot water temp. throughout the house isn't what I consider "really hot" (meaning too hot to touch for more than a second or two).

- The thermostat is turned up to it's highest setting.

- These observations are true both day and night, though the water does warm-up slightly faster at night.

- The house is about six years old, and is a single story (~2100 sq. ft.).

Any ideas what might be the problem? Is the thermostat broken? Does the house need a more powerful water heater? Is there something wrong with the lines?

"But when the additional outlets are shut-off, the maximum temp. of the hot water decreases."

Unless you have an extremely long run and it is really cold, it is not reasonable for the water to be substantially cooler the farther you get from the heater or to cool down when other faucets are shut down. Instant hot water will not happen unless you have a recirc system (so don't expect it). The water in the hot lines cools down. When you have 2 or more taps open, it puts out more water and the hot water gets to you faster.
I think that I would be first checking for a single handle faucet, a tempering valve, or a cross connection between the hot and cold that is allowing cold water to enter the hot line. Then check that both thermostats and both elements are working properly. If you have had residue and debris (usually white) you could need a new dip tube. Thermostats that are turned up all the way, but not producing hot water,usually indicates a thermostat or
This may be beyond your ability to diagnose. I often tell people that they sometimes pay me more for what I know than for what I do. Often, the repair is the simple part of the job, diagnosing the problem can sometimes be tough. Or you can have multiple problems.
Deb
The Pipewench